#1060 - Missing Element in Sorted Array

Medium • View on LeetCode • View on GitHub

Problem Description

Given an integer array nums which is sorted in ascending order and all of its elements are unique and given also an integer k, return the kth missing number starting from the leftmost number of the array.

Solution

/**
 * @param {number[]} nums
 * @param {number} k
 * @return {number}
 */
var missingElement = function(nums, k) {
  const n = nums.length;

  if (k > getMissingCount(n - 1)) {
    return nums[n - 1] + k - getMissingCount(n - 1);
  }

  let left = 0;
  let right = n - 1;

  while (left < right) {
    const mid = Math.floor((left + right) / 2);

    if (getMissingCount(mid) < k) {
      left = mid + 1;
    } else {
      right = mid;
    }
  }

  return nums[left - 1] + k - getMissingCount(left - 1);

  function getMissingCount(index) {
    return nums[index] - nums[0] - index;
  }
};